The present invention relates to ink jet printing apparatus of the type described in our prior U.S. Pat. Nos. 5,969,733, 6,003,980 and 6,106,107, and also in our prior International Patent Application No. PCT/IL02/00346 filed May 3, 2002, published on Nov. 14, 2002 as International Publication No. WO 02/090119 A2, the contents of which patents and application are incorporated herein by reference.
Ink jet printers are based on forming droplets of liquid ink and selectively depositing the ink droplets on a substrate. The known ink jet printers generally fall into two categories: drop on-demand printers, and continuous-jet printers. Drop on-demand printers selectively form and deposit the ink jet droplets on the substrate as and when demanded by a control signal from an external data source; whereas continuous-jet printers are stimulated by a perturbation device, such as piezoelectric transducer, to form the ink droplets from a continuous ink jet filament at a rate determined by the perturbation device.
In continuous-jet printers, the droplets are selectively charged and deflected to direct them onto the substrate according to the desired pattern to be printed. In binary-type printer systems, the droplets are either charged or uncharged and, accordingly, either reach or do not reach the substrate at a single predetermined position. In a multi-level system, the droplets can receive a large number of charge levels and, accordingly, can generate a large number of print positions. Both types of systems generally include a gutter for receiving the ink droplets not to be printed on the substrate.
The present invention is particularly applicable to continuous-jet printers and is therefore described below with respect to this application. It will be appreciated, however, that aspects of the invention could also be used in droplet-on-demand printers or in other applications.
The conventional continuous-jet printer of the type described in the above-cited patents and International Application comprises a linear array of jet modules each including an inlet for receiving: ink, an outlet for re-circulating the ink, a nozzle for discharging ink in the form of droplets, and a perturbation device, such as a piezoelectric transducer, for causing a continuous stream of droplets to be discharged from the respective nozzle. Such apparatus further comprises an ink supply system including an inlet manifold, an outlet manifold, and a plurality of connecting passageways connecting the jet module inlets in parallel between the inlet and outlet manifolds. In one prior art construction of such printing apparatus, the connecting passageways define an F-connection of each jet module with the inlet and outlet manifolds.
Such a prior art construction is more particularly described below with respect to FIGS. 1–4 of the accompanying drawings. One drawback in such a prior art construction is that the jet modules have relatively large mass which undesirably affects the printing resolution. Thus, for high quality printing, it is desirable to print with very small ink droplets, at relatively high frequencies, and with relatively close spacings between the jet modules. Jet modules with relatively high masses, such as in the prior art construction illustrated in FIGS. 1–4, limit all three of the above objectives for high quality printing.
Another drawback in the prior art construction illustrated in FIGS. 1–4 is the tendency of the nozzles to become clogged, and the difficulty in cleaning the nozzles at the printing site without requiring major disassembly of the jet modules.